1. Field of the Invention
The present invention relates to a rotation transmitting apparatus which can transmit rotation from an input side to an output side while changing a transmission ratio in a stepless manner and which is used for, for example, changing a correspondence between an operation amount of a steering member and that of a steering mechanism in a steering apparatus for a vehicle.
The present invention also relates to a vehicle steering apparatus in which an input shaft connected to steering means and an output shaft connected to a steering mechanism are interlockingly coupled to each other by a differential mechanism.
2. Description of Related Art
A steering operation of a vehicle is performed as follows. That is, a rotating operation applied to a steering member is transmitted to a steering mechanism via a column shaft, and the steering mechanism converts the rotating operation to a linear operation in a left-and-right direction of the vehicle, thereby changing a direction of wheels. In the case of performing such a steering operation, when the vehicle runs at low speed, a steering controlling operation amount of the wheels is made larger than a rotating operation amount of the steering member. In contrast, when the vehicle runs at high speed, the steering controlling operation amount of the wheels is made smaller than the rotating operation amount of the steering member. This can facilitate a driving operation at low-speed running, and can enhance stability at high-speed running.
Consequently, there has been practically used a steering apparatus in which a rotation transmitting apparatus for changing a transmission ratio to transmit rotation is arranged in a middle portion of a column shaft for coupling a steering member and a steering mechanism to each other, and which can transmit the rotation from the steering member side as an input side to the steering mechanism side as an output side while changing the transmission ratio. In addition, there has been practically used, for example, a rotation transmitting apparatus which includes a planetary gear mechanism and a motor for changing a rotational speed, and can change a transmission ratio in a stepless manner.
Japanese Utility Model Examined Publication No. 06-2860 (1994) proposes a steering apparatus which uses a planetary gear mechanism including a sun gear, a planetary gear and an internal gear. Herein, an input shaft is fixed to the sun gear, an output shaft is fixed to a carrier which couples a rotation shaft of the planetary gear, a motor for rotating the internal gear is provided, and a rotational speed of the internal gear is controlled, so that a transmission ratio of rotation from the input shaft to the output shaft is made variable. In this steering apparatus, if the internal gear is rotated in the same direction as a rotational direction of the input shaft by the motor, a rotational speed of the output shaft can be increased in accordance with a rotational speed of the internal gear. In contrast, if the internal gear is rotated in a reverse direction of the rotational direction of the input shaft, the rotational speed of the output shaft can be decreased in accordance with the rotational speed of the internal gear.
In addition, Japanese Patent Application Laid-Open No. 2002-240730 proposes a steering apparatus including a first internal gear rotating with a steering member, a first sun gear, a first planetary gear meshed with the first internal gear and the first sun gear, a second internal gear rotating with an output shaft, a second sun gear, and a second planetary gear meshed with the second internal gear and the second sun gear. Herein, the first sun gear and the second sun gear are rotated by a motor as a unit, so that a transmission ratio of rotation is made variable. In this steering apparatus, rotation of the first internal gear is transmitted to the second internal gear through rotational motion on their axes and orbital motion of the first planetary gear and the second planetary gear. At this time, if the sun gears rotating with each other are rotated in the same direction as a rotational direction of the first internal gear by the motor, a rotational speed of the second internal gear can be increased in accordance with a rotational speed of the sun gears. In contrast, if the sun gears are rotated in a reverse direction of the rotational direction of the first internal gear, the rotational speed of the second internal gear can be decreased.
On the other hand, a vehicle steering apparatus having a differential mechanism includes a sun gear provided to an input shaft connected to a steering wheel, a planetary gear meshed with the sun gear, a carrier arranged in coaxial with the sun gear and supporting the planetary gear so as to orbit around the sun gear freely, an output shaft coupled to a center portion of the carrier and connected to a steering mechanism, an internal gear rotating freely in coaxial with the output shaft and meshed with the planetary gear, and a differential electric motor having a drive gear meshed with an external toothed member provided on an outer periphery of the internal gear. Herein, when the steering wheel is operated, the steering mechanism is operated via the input shaft, the sun gear, the planetary gear and the output shaft. When the electric motor is driven, the internal gear is rotated, and the steering mechanism operates while increasing its operation speed via the output shaft connected to the carrier (see, for example, Japanese Patent Application Laid-Open No. 2003-312486).
The vehicle steering apparatus disclosed in Japanese Patent Application Laid-Open No. 2003-312486 also includes a first detector which detects a rotational angle of the input shaft, and a second detector which detects a rotational angle of the output shaft. Herein, drive circuits of first and second electric motors are controlled on the basis of values detected by the first and second detectors, and the like, and the rotational angle of the output shaft is compensated with respect to the rotational angle of the input shaft.
There has been also known a vehicle steering apparatus including a differential mechanism and a differential electric motor. Herein, the vehicle steering apparatus includes an input shaft connected to a steering wheel and provided with a transmission gear, an output shaft interlockingly coupled to a drive gear meshed with the transmission gear, and a reaction force electric motor applying a required torque to the input shaft in accordance with a torque applied to the output shaft. The reaction force electric motor is driven in the case where a steering torque applied to the input shaft is changed from an appropriate steering torque, for example, the output shaft is rotated while increasing its rotational speed by the differential electric motor. In addition, the reaction force electric motor applies a required torque to the input shaft in accordance with a torque applied to the output shaft, and corrects the torque so as to obtain an appropriate steering torque.
However, each time a running direction of a vehicle is changed, rotational directions of a steering member and column shaft are switched in the vehicle steering apparatus. Therefore, if a planetary gear mechanism is used in the steering apparatus, there arises a problem that an abnormal sound generates at mesh portions of the respective gears upon switching of the rotational directions. This abnormal sound is a collision sound generated when teeth of the respective gears are relatively moved within a range of backlash upon switching of the rotational directions and then are collided with each other. In addition, there is also generated a sliding sound generated when a gear is operated.
In the steering apparatus disclosed in each of Japanese Utility Model Examined Publication No. 06-2860 (1994) and Japanese Patent Application Laid-Open No. 2002-240730, at a mesh portion of the sun gear and the planetary gear and a mesh portion of the planetary gear and the internal gear, teeth of the respective gears are collided with each other, so that an abnormal sound generates. In addition, since the steering apparatus has a construction that three types of gears: a sun gear, a planetary gear and an internal gear are meshed, there arises a problem that a planetary gear mechanism becomes large in size, resulting in increase of the number of components and the number of assembling processes. In the steering apparatus disclosed in Japanese Utility Model Examined Publication No. 06-2860 (1994), another gear mechanism is used for transmission of rotation of a motor; therefore, there arises a problem of generation of an abnormal sound at a mesh portion in this gear mechanism.
In the vehicle steering apparatus including the differential mechanism as disclosed in Japanese Patent Application Laid-Open No. 2003-312486, further, it is necessary to provide the first detector for detecting the rotational angle of the input shaft and the second detector for detecting the rotational angle of the output shaft, there arises a problem of increase in cost of the vehicle steering apparatus due to cost of the detectors, the assembling work for the detectors, and the like. There also arises a problem that it is difficult to ensure an arrangement space of the vehicle steering apparatus in the case of mounting the apparatus onto a vehicle.
Also in the vehicle steering apparatus including the differential mechanism, the differential electric motor and the reaction force electric motor, it is necessary to provide a first detector for detecting a rotational angle of an input shaft and a second detector for detecting a rotational angle of an output shaft, resulting in the same problems as those in Japanese Patent Application Laid-Open No. 2003-312486.